A filter assembly for an air purifier is largely classified into a filter for removing particulate matter, and a filter having sterilizing and deodorizing capabilities.
Examples of the particulate matter removing filter include a pre-filter, a medium filter, a high efficiency particulate air (HEPA) filter, an ultra-filter, and so on.
The pre-filter is capable of removing dust particles having a size equal to or greater than 5 □, and is made of a polypropylene sheet or non-woven fabric.
The medium filter is a filter having filtering efficiency of 40 to 95% and ranking 9 to 16 by maximum expiratory flow volume (MEFV), as particulate matter having a particles size of 1 to 3 □, as tested by the Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) Standard. Inorganic fiber such as glass fiber and artificial fiber such as synthetic fiber are used as the medium filter. In recent years, however, due to several disadvantages resulting from the use of glass fiber, such as flyash of fibrous glass dust or a high pressure loss, synthetic fiber has become widely used.
As tested under the same standard requirements as the medium filter, the HEPA filter (or ultra-filter) is turned out to be a highly efficient filter, that is, having filtering efficiency of 99.97% or greater (99.999% for ultra-filter) and ranking 17 by MEFV, using glass fiber or synthetic fiber. For the same reason as in the medium filter, synthetic fiber is typically used for air purifier purposes.
Meanwhile, as the filter having sterilizing and deodorizing capabilities, a catalyzing filter is typically used. The catalyzing filter is configured to remove air-borne microorganisms such as viruses, E. coli, fungi, odor-generating substance, a variety of organic materials, germs, environmental hormones, and so on, by coating materials capable of performing a photocatalytic action on a metallic or fabric plate. A photocatalyst useful in such a catalyzing filter is a material that exhibits a powerful oxidizing effect when UV light having band-gap energy of approximately 3.2 eV is irradiated at a wavelength of about 400 nm or less, a representative useful example thereof is titanium dioxide (TiO2).
When titanium dioxide is irradiated with UV light, electrons and holes are generated, the electrons and holes both having strong reducing and oxidizing effects. Particularly, the holes react with water and dissolved oxygen to generate hydroxyl (OH) radicals and free radicals called reactive oxygen species (ROS). Since the energy of the hydroxyl (OH) radicals is higher than the band-gap energy of molecules forming the organic matter, photocatalytic reactions using titanium dioxide (TiO2) are employed in a wide variety of applications associated with environmental purification, including decomposition/conversion of contaminant chemical substance, various volatile organic compounds (VOCs), and so on.
However, since conventional catalyzing filters, either in industrial use or home use, exhibit sterilizing and disinfecting actions only through a photocatalytic reaction, the sterilizing and disinfecting capability of the catalyzing filter is determined by a reaction between photocatalyst materials. However, if suspended particulate matter is deposited on the photocatalyst materials, the reaction is retarded, resulting in an increase in a constant pressure, ultimately involving high power cost and requiring frequent filter replacement. In addition, the conventional catalyzing filters cannot provide for sterilizing and disinfecting capability when a lamp is not driven due to temporary power interruption or a lamp OFF driving in regular ON/OFF switching cycles.
Further, a general plate-type catalyzing filter is not length-adjustable with respect to lamps having variable lengths.